barrelling is a term borrowed from
long-standing United States political practice.
As that hyperlink shows, it is associated
with electoral systems where candidates likely to
form part of a government who are standing in
closely-contested 'marginal' electoral districts
seek electoral benefit by promising substantial
spending if they are elected and their party
becomes the government party. Most districts are
not marginal, instead being safe for one of the
two major electoral groupings in such contests.